Channel layer chromatorgraphy



Sept. 9, 1969 M. J. MATHERNE, JR

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United States Patent O 3,465,884 CHANNEL LAYER CHROMATOGRAPHY Mederic J.Matheme, Jr., New Orleans, La., assigner to the United States of Americaas represented by the Secretary of the Department of Health, Education,and

Welfare Filed Sept. 2S, 1967, Ser. No. 670,131 Int. Cl. B01d 23/10,15/08 U.S. Cl. 210-323 7 Claims ABSTRACT OF THE DISCLOSURE Thisinvention relates to new chromatographic devices and relates moreparticularly to a development which may be referred to as channel layerchromatography.

Numerous chromatographic procedures are presently known among the morecommon of which are column chromatography .and thin layerchromatography. Column chromatography is frequently desirable because ofits high capacity for product material, but this technique suffers fromnumerous well-known disadvantages. For example, column chromatography isrelatively slow, frequently requiring from one-half hour to as much as afull day for an adequate separation. Further, this procedure requiresrelatively high volumes of chromatographic solvent. These twoconsiderations alone, that is, high time and solvent requirements,render column chromatography relatively undesirable for certainapplications.

In contrast to column chromatography, thin layer chromatography is arelatively high speed procedure generally requiring from only 10-20minutes for an individual separation. Further, this technique utilizesminimal quantities of chromatographic solvent. However, thin layerchromatography suffers from the critical disadvantage that it has almostno usable product capacity whereby its applications are extremelyrestricted. In order to obtain even minimal product capacity with thinlayer chromatography, the samples must be smeared over an extremely wideportion of a plate thereby making subsequent analyses extremelydifficult.

Thus, it will be seen that there ,are sorne significant limitations onthe use of these prior art chromatographic techniques from thestandpoint of either cost in time or materials, or product capacity.

Another disadvantage inherent in both of the above prior artchromatographic techniques as they are presently practiced is thedifficulty encountered in running large numbers of individual samples orin running samples and controls therefor under at least substantiallyindentical environmental and processing conditions. Since columnchromatography and thin layer chromatography are each only primarilyadapted for individual separations, duplication of equipment andprocessing variables encountered in multiple separations as presentlypracticed by either of these procedures renders them relativelyinefficient and unreliable.

The instant inventive concepts combines the advantages ICC of column andthin layer chromatography while overcoming the `aforementioned and otherdisadvantages inherent in each technique. Specifically, it is a primaryobject of this invention to' provide chromatographic devices which offera product capacity comparable to column chromatography, but whichfunction at speeds comparable to thin layer chromatography. Further, itis `a basic object of this invention to provide for chromatographicdevices which are extremely compact and simple to utilize requiring lesschromatographic solvents than prior art devices and procedures ofcomparable capacity.

The instant inventive concepts also provide chromatoggraphic techniqueswhich reduce health hazards to personnel from exposure to solvents,topically or by inhalation and which similarly reduce exposion and firehazards.

Additionally, and with particular reference to the background set forthabove, it is an important object of this invention to providechromatographic devices which permit simultaneous separation of numerousproduct samples under at least substantially identical processingconditions in a simple, inexpensive, highly efficient and reliablemanner.

The instant inventive concepts are broadly useful as a newchromatographic separation technique in general and in any analyticalarea where such procedures are ordinarily found. In effect, thisinvention provides for chromatography in a form which is distinct fromexisting techniques such as the column and thin layer chromatographymentioned previously as well as other conventional chromatographicprocedures such as paper chromatography, gas chromatography and the likeand may be said to be a general tool for chemical analyses which affordschromatographic separations of chemicals or materials which ,are presenttogether in a mixture.

Although, as has been stated immediately hereinabove, the instantinventive concepts are not to be limited to a particular application,one area is which various chroma.- tographic procedures have beenutilized extensively hereinbefore, and wherein the devices .andprocedures of the instant invention are believed to be particularlyuseful, is the separation of pesticide residues from co-extracted plantmaterial. Thus, a special object of this invention is the provision of anew cleanup procedure for pesticide residue analysis which may beutilized as `a primary cleanup procedure in this field or to supplementother presently existing cleanup procedures.

Other and further objects of the instant invention reside in thecombination of elements, arrangement of parts and features ofconstruction of the devices set forth hereinafter, as well as thespecific manipulative Steps and materials utilized in the procedureshereof.

Still other objects will in part be obvious and in part be pointed outas the description of the invention proceeds and as shown in theaccompanying drawing wherein:

FIGURE 1 s a perspective view of a preferred embodiment of a channellayer chromatographic plate in accordance with the instant inventiveconcepts prior to filling the channels thereof with chromatographicadsorbent material;

FIGURE 2 is a front elevational view of the plate of FIGURE 1 showingthe channels thereof filled with chromatographic adsorbent material;

FIGURE 3 is a bottom edge elevational view of the plate as shown inFIGURE 2; and

FIGURE 4 is a schematic fiow diagram showing the use of the instantinventive concepts as a cleanup procedure for pesticide residueanalyses, only a single channel layer strip being illustrated forconvenience.

Like reference characters refer to like parts throughout the severalviews of the drawing.

Referring now to the drawing in general, and more particularly toFIGURES 1-3, a channel layer chromatographic plate in accordance with apreferred embodiment of the instant invention concepts is designatedgenerally by the reference numeral and will be seen to comprise a commonplate or support element 12 in which has been defined in anyconventional manner a plurality of substantially parallel spacedchannels 14 extending from the top edge 16 to the bottom edge 18thereof. The channels 14 are filled in a manner to be more fullydescribed hereinafter with a chromatographic adsorbent material toprovide a plurality of discrete channel layer strips 20.

In the embodiment shown, the support member 12 is formed of glass and issubstantially square with rectangular channels defined as depressions inone major face thereof. However, these details are not in any waycritical and may be varied substantially. For example, the supportmember 12 may be formed of any suitable alternative solid materialincluding various plastics or metals which would not be subject toattack by the particular chemicals to be utilized in the chromatographicprocessing. Similarly, the size and shape of the support member 12 canobviously be readily modified, although a flat, 8 inch by 8 inch by l/4inch plate has been found to be particularly useful. Likewise, therelative dimensions of the channels 14 are also obviously subject tosignicant variation without departing from the instant inventiveconcepts. In the preferred embodiment shown, nine channels, each 10millimeters wide and Z millimeters deep have been utilized. The onlysignificant factor in these dimensions is the depth which provides forchannel layer strips 20 substantially thicker than the ordinary M4 to V2millimeter thickness of adsorbent generally utilized in conventionalthin layer chromatography. The individual channels can, in fact, be evensubstantially deeper and wider according to this invention, for example,up to 10 millimeters deep and 3-5 centimeters wide each. In any event,however, to provide significantly greater product capacity, theindividual channels should have a depth over a major portion of thewidth of the same, at least in excess of 1 millimeter and preferably atleast about 2 millimeters. This significantly greater thickness ofadsorbent in each of the channel layer strips 20 in and of itselfdistinguishes the chromatographic dev-ice of the instant invention froma thin layer chromatographic plate and provides for substantial increasein product capacity, an important feature of the instant invention.

Although the preferred channels 14 have been shown as rectangular incross-section and uniformly filled by adsorbent throughout their length,it will be understood that other shapes are well within the instantinventive concepts. For example, the channels can be square incross-section. Alternatively, they may be V or U-shaped with the angleof the V or rad-ius of the U, as Well as the depth and surface width ofthe channels varying depending upon the intended use. Further, thedimensions of the channel need not be uniform over the entire length ofthe support plate, but rather, for example, the channels can be slopedto provide a greater depth at one end of the plate than at the other. Inthis same vein, although the channel layer strips 20 must be continuousover the length of the channels 14, the thickness of the adsorbentmaterial, in contrast to the channels themselves, may be diminishedtoward the top of the channels or the adsorbent material may be steppeddown in thickness toward the top of the plate member. Reduction of thethickness of the channel layer strips toward the top of the sameprovides maximum product capacity at the bottom or lower end withmaximum separation at the top or upper end.

Moreover, although the channels 14 have been illustratively shown asdepressions or recessions in one of the major faces of the plate member12, they can be cornpletely embedded within the plate member except forthe open opposite ends. For example, the channels can be defined bylongitudinal bores through the plate member from one edge surface to anopposite edge surface, either cylindrical or of any other desiredcross-section. Additionally, the channels can be in the form of boreswhich taper in cross-section from one end of the plate member to theother. Although such closed channel embodiments are feasible andpossibly even desirable for certain applications, they are notcontemplated for ordinary use and the open-surface channels as shown inthe drawing are preferred. With closed channels, only a portion of thechannel can be filled with adsorbent material, followed by applicationof the test sample and then completion of the channel filling.Similarly, removal of the solvent front portion of the adsorbent wouldhave to be effected by pressing the channel layer strip out of one endof the channel from the opposite end. These difficulties in preparationand use of the closed channel embodiments evidence the more limitedapplication of such constructions.

The above-described modifications are merely set forth as illustrativeand are not shown in the drawing since numerous other configurations forthe channels would be readily recognized by those skilled in the art`Thus, the basic and significant characteristics of the channels are:

(l) There are a plurality of them, that is, two or more-this permitssimultaneous multiple separations;

(2) They are parallel to each other; and

(3) They each have a lower open end communicating with a rectilinearportion of the bottom edge of the plate member whereby these open endsof the channels may be said to be coplanar, with the channels generallyperpendicular to the rectilinear bottom edge portion.

The basic techniques for preparing and utilizing a channel layerchromatography device such as the element shown at 10 in the drawingwill be better understood by reference to the following specificexamples.

EXAMPLE 1 Preparation of channel layer chromatographic plate Place 60grams of aluminum oxide G such as is available for thin layerchromatography from Brinkmann Instruments, Inc. into a 12S ml.glass-stoppered flask. Add 50 ml. distilled water, stopper, and shakevigorously (ca. 30 sec.) until slurry is no longer watery. Too muchwater in the slurry will cause the adsorbent to crack and/or contractaway from the sides of the channels. The ratio of A1203 may need to bevaried for some batches of A1203. If slurry is too thick, correct by (a)shortening shaking period to 15-20 sec.; (b) increasing volume ofdistilled water by 5-10 ml.; or (c) combining (a) and (b). Immediatelypour slurry evenly across middle of plate, at right angles to channels.Spread slurry into channels with the aid of a metal spatula.

It is easier to prepare the channel layer plate if the channels arefirst covered at each end of the plate. This may be done with maskingtape A or with aluminum foil B:

A. Place strip of masking tape, adhesive side up, on work bench; placeedge of plate (with ends of channel layer grooves) even with long edgeof tape. Smooth excess tape onto back, or underside, of glass plate. Thetape now forms a Wall which prevents the slurry from running out of thechannels. Remove tape when adsorbent is no longer fluid enough to runout of channels.

B. Place plate on aluminum foil, turning up edges of foil at each end ofplate. The slurry is prevented from running out of the channels by thealuminum foil at each end.

After the slurry has been spread into the channels, let

5 the plate dry 36-48 hours at room temperature and then store in thedark.

Scrape of excess adsorbent with a razor blade, using ridges betweenchannels as a guide. The ridges should be clean of adsorbent and thechannels should contain adsorbent level with the ridges. Trim one end ofeach channel layer (along edge of plate that is to be the bottom) sothat a smooth, flat surface or edge will be presented to `thechromatographing solvent.

The use of a plate prepared in the manner f Example 1 will now bedescribed with particular reference to FIG- URE 4 and a cleanupprocedure for pesticide residue analysis.

EXAMPLE 2 Sample extraction Prepare and extract product according toMills et al.1 as edited in compilation by Barry et al?. Proceed to pointwhere pesticides have been partitioned from acetonitrile extract intopetroleum ether, and water has been removed with Na2S04. Evaporatemeasured petroleum ether extract in Kuderna-Danish apparatus to ca. 5ml. Continue evaporation to 2 ml. on heating block at 37 C. or in beakerof warm water (held at 35-40 C.), using stream of clean, dry air.

Application of product extract onto channel layers Several samples ofthe same product extract may be applied to selected channels in a singleplate. Alternatively, or additionally, control or standard materials aswell as other product extracts may be run simultaneously on differentchannels in a single plate. For simplicity of illustration only a singlechannel layer strip has been shown in FIGURE 4, although it will beunderstood that a plurality of chromatographic separations are runsimultaneously according to the instant inventive concepts.

Apply an appropriate volume of product extract (ca. -20 g. sample) tothe channel layer, with a 100 nl. or other suitable syringe. Volumes of500 al. and 1 ml. have been applied without difiiculty.

Apply extract evenly over a -25 mm. length of the channel layer stripfrom lateral edge to edge, about 15-20 mm. from the bottom edge (seeStep l, FIGURE 4). The rate of application is governed by the speed atwhich the solvent penetrates the adsorbent. Do not let the solventextract migrate onto the glass surface adjacent to the channel layer.Wash the extract down into the channel layer strip by applying 100-200nl. petroleum ether to the area of application.

Chromatographing the applied product extracts Add ca. 40 ml. of a i+1mixture of acetonitrile and tetrahydrofuran to a trough on the bottom ofa conventional chromatographic tank and place the channel layer plate inthe tank. Do not saturate the tank before inserting the plate. Positionthe bottom edge of the plate (bearing evenly trimmed channel layer stripedges) in the glass trough so that the solvent is in contact with eachchannel layer strip, but does not touch the applied sample extract.Cover the tank and let the solvent rise ca. Fys to 3A of total height ofthe channel layer strips. Remove the plate and mark solvent front with agrease pencil on the clean glass ridges adjacent to the channel layerstrips or on the back of the plate, and air-dry in a hood (ca. min.).

Re-chromatograph as before, using acetonitrile only. Let this solventfront go about 15-20 mm. above the first solvent front. Remove the plateand mark the second solvent front. Air-dry about 20 min. (see Step 2,FIGURE 4). Solvent fronts may vary with the individual channels, sincethey depend upon the products, the amount applied and the ability of thesolvents to penetrate it. Solvent fronts may migrate with someadsorbents after removal of the plate from the tank.

1Chnnges in Methods. JAOAC, 49. p11. 20G-250 (1066). '-PestcideAnalytical Masual, vol. I, Barry et al., FDA (19H5) Removal of theisolated pesticide residues from the channel layer strip Quantitativelyremove the channel layer adsorbent from 4-7 mm. above the secondmigrated front, if migration occurs, to 4 mm. below the firs-t solventfront. The section of the channel layer strip within the two solventfronts contains the pesticide residues extracted from the product (seeStep 3, FIGURE 4).

With a thin blade-like instrument, remove and discard the channel layermaterial which is more than 4-7 mm. above the second solvent ormigration front. Quantitatively remove the next section to about 4 mm.below the first solvent front, by scraping same into a small beaker.Powder the material and quantitatively transfer the same to a microfunnel containing a glass wool plug (see Step 4, FIGURE 4). Elutepesticides from the micro funnel with l0 ml. petroleum ether into asmall graduated cylinder. Concentrate the eluate at 37 C. if necessary.Inject an appropriate volume of the eluate into conventional gaschromatograph for the determinative Step (see Step 5, FIGURE 4) Thetechniques and materials step forth in Examples l and 2 above, asindicated, are merely illustrative and may be readily modified withinthe skill of the art. For example, although aluminum oxide G has beenutilized as the chromatographic adsorbent, other well-known materialsmay be readily substituted therefor. For example, in place of aluminumoxide G, slurries may be formed of silica gel, plaster of Paris or thelike. The basic significant factor regarding the adsorbent material, inaddition to its adsorbent properties, is its capillary properties. Inother words, the material utilized to fill the channels must be capableof drawing chromatographic solvent up past the limited zone to which theproduct extract has been applied so as to form a solvent front therebysegregating various materials from the product extract mixture.

In order to further appreciate the capacity and efficiency of thechannel layer chromagraphic cleanup technique of the instant inventionthe following illustrative examples should be considered:

EXAMPLE 3 Low levels of various pesticides were extracted quantitativelyfrom a large amount of notorious" plant material in a channel layerplate of the preferred dimensions set forth hereinabove and formedaccording to the preferred techniques of Example 1. Four products whichhad previously been found to be free of pesticide residues at low levelsof detection were chosen: (l) peanuts-a high fat food not routinelyextracted with acetonitrile was chosen to provide oil for the composite;(2) onionsan extremely dirty product by any cleanup method was chosen toprovide the volatiles for the composite; (3) carrots-cleanup with aconventional Florisil column showed that the second eluate (15%)contained interfering response on electron capture gas-liquidchromatography; and (4) cabbage-cleanup with Florisil showed that therst eluate (6%) contained a large, early response interference onelectron capture gas-liquid chromatography and a large sulfur responseby microcoulometric gas-liquid chromatography.

Equal amounts of these four comminuted products were combined in ablender and extracted with acetonitrile. Portions of the acetonitrileextract were fortified with low levels of aldrin, dieldrin, endrin, andthiodan, alone and in combination. The fortified acetonitrile portionswere then evaporated to a small volume and a quantity of each fortifiedacetonitrile extract equivalent to l5 grams of the composite plantmaterial was applied directly to the channel layer strip. Excellentrecovery of these pesticides at the 0.02, 0.03, and 0.04 p.p.m. levelsdemonstrates the ability of this cleanup procedure (see Table l).

TABLE L RECOVE RY OF PESTICIDES ADDED TO CRUDE ACETONITRILE EXTRACT OFCOMPOSITE 1 AND SPOT- TED DIRECTLY N CHANNEL PLATE l Composite ofpeanuts, onions, carrots, and cabbage.

2 Each portion spotted was equivalent to 15 g. of the composite.

Table 2 shows a comparison of pesticides found to be present on a numberof fruits and vegetables analyzed by using Florisil and then bysubstituting channel layer chromatography for the Florisil cleanup inthe normal scheme.

TABLE 2.-COMPARISON 0F PESTICIDE RECOVERIES (P.P.M.) AFTER CLEANUP WIT HFLORISIL COLUMN AND CHANNEL LAYER CHROMATOGRAPIIY Cleanup procedurePesticides Florisil Product l detected column C LC StrawberriesHeptachlor 0. 005 None Dieldrin and 0.005 or' 0005 of Aldrin. each eachToxapheue D. 28 0. 74 l). 4ii l). 37 0. 005 N one 0. 24 0. 10 \0. 005 0.005 None 0. 0G 0. 005 0. 005 Toxaphene 0. 16 0. 17 DDT N011@ 0. 005Celery DDT None t).

- 2 0. 1L Squash Dieldiin 2 0 18 i 0. 14 Parsley DDT 531%; 11. 8 PeachesDDT 0. 38 0. 41 Apples Dieldrin D. 013 0. .121

1 In three strawberry samples and one cucumber samplc no pesticides weredetected with either cleanup.

l 0.15 average.

l 9.4 average.

Table 3 represents a number of fruits and vegetables with addedpesticides. These products were fortified with known quantities ofvarious pesticides after the petroleum ether extraction step. In thisway, the efciency of the cleanup for individual products could betested.

TABLE 3,-RECOVERY OF PESTlCIDES FROM FORTIFIED ETRACTS OF VARIOUSPRODUCTS WITH THE CHAN- EEIELAYER CHROMATOGRAPHY CLEANUP PROCE-Recovered Added, Product Pesticide ppm. P.p.m Percent Onions Aldrin O.050 (l) Heptachor 0. 050 0. 052 104 epoxide. Mustard gre/ens. Aldrn 0.050 0. 052 104 Heptachlor 0. 050 0. 049 'J8 epoxide. Potatoes Aldrin 0.l). 041 82 Heptachlor 0. 050 l). 030 78 epoxide. Green beens Aldrin 04050 0. 051 102 Heptachlor 0. 050 0. 050 112 epoxide. Grapes Chlordano 0.034 0. 038 112 Apples Lindane 0. 040 0. 031i J0 Hentachlor 0. 040 0. 034S5 Aldrin 0. (Hit) 0. 055 92 DDT 0.080 tl. 004 118 Tomatoes .Y DDT 1.621.81 112 Turnips Aldrin 0. 060 0. 052 87 Dieldrin l). 080 0. 077 litiThiOdan 0. l2 0` 105 88 Endriu 0. 080 0. 082 102 not peppers lleptachlor0. 060 0.057 .15

epoxide. Dieldrin 0. 0. 082 82 l Peak masked by crop on gas-liquidchromatogram.

Of the nine products tested, only onions showed interference. Crop peaksmasked the detection of aldrin but permitted calculation of theheptachlor epoxide added. For this product, it may be necessary toreduce sample size taken for cleanup or to rechromatograph on channellayer chromatography a second time to detect early eluting pesticides.

This cleanup procedure has also been used successfully to replace thesaponification and MgO-Celite column cleanup of the 15 percent eluatesof seven soybean samples prior to confirmation by thin layerchromatography as will be seen in Table 4.

Endrln (ppm.) in 15% eluate Thin layer chromatography, after chan-Gas-liquid chroma tography, no adnel layer chromatog- Sample ditionalcleanup raphy cleanup Channel layer chromatography, on aluminum oxide Gin the form of discrete 8" strips, 2 mm. thick by 10 mm. wide, retardsthe movement of plant extractive but has little or no effect on themigration of pesticides. Chlorinated organic insecticides respondimmediately to the rising solvent front and move with the front in theform of a tight band or line. This was illustrated by a limitedexperiment where the channel layers were dissected and treated withsilver nitrate to locate the position of the chlorinated pesticides.Plant extractives retard this movement only slightly. Because of this,the channel layer strips were chromatographed twice to insure that thepesticide residues are quantitatively present at the solvent front.

Tetrahydrofuran, an organic solvent with properties similar toacetonitrile, Ibetter penetrates the plant material and extracts thepesticide from it in the initial development. However, whentetrahydrofuran was used alone, too much plant material was carried intothe area containing pesticides; acetonitrile alone is desirable for thesecond development step because of its selective preference forpesticides.

Occasionally plant pigments rose up the channel layer strips closebehind the solvent front. After re-chromatographing, the pigmentationwas contained in the section of the adsorbent to be removed, i.e., thesection which contained pesticide residues. Generally the pigmentationdid not hinder the electron capture gas-liquid chromatographdeterminative step, although it sometimes discolored the eluate. Noevidence of the pigment was found on the gas chromatogram.

The aluminum oxide G used is in the non-activated state, that is, it ismixed with water, applied to the channel layer chromatography plate andair-dried. Activation of the channel layer strips with heat C.)R priorto use will stop the movement of all pesticides and plant material.Prepared plates were stored open, in the dark, and were used up to fourweeks after preparation.

The normal Florisil cleanup procedure 3 uses two eluting solvents forthe purpose of isolating dieldrin and endrin from other chlorinatedorganic pesticide residues.4 When the channel layer chromatographycleanup is substituted for the Florisil cleanup in this procedure,dieldrin and endrin residues are recovered together with all chlori- 3Changes in Methods, JAOAC, 49, pp. 20G-250 (1966). 4Jo1inson, JAOAC, 45,pp. 363-365 (1962).

nated organic pesticide residues present. Because of this, there may betimes when the nonpolar gas chromatographic column used in this studywill not be able to separate certain specific pesticides. In suchinstances, adequate separation of these pesticides can be achieved byusing the polar column recommended by Burke and Holswade.5

In addition to separation of the chlorinated pesticides set forthhereinabove, channel layer chromatography according to the instantinventive concepts has been utilized in the separation ofnon-chlorinated pesticides such as Sevin, l-naphthyl N-methyl carbamateas Well as organic phosphate pesticides such as parathion and malathic.Addionally, this technique has been utilized in the separation of themedicinal -components from medicated animal feeds, such as, for example,nitrofurazone and furazolidone. These illustrative chromatographicseparations will provide some appreciation for the broader applicationsof channel layer chromatography.

It will now be seen that there are herein provided new and improvedchromatographic devices which satisfy all of the objectives of theinstant invention, and others, including many advantages f greatpractical utility and commercial importance.

Since many embodiments may be made of the instant inventive concepts,and since many modifications may be made of the embodiments hereinbeforeshown and described, it is to be understood that, unless otherwisespecitied, all material herein is to be interpreted merely asillustrative and not in a critical sense. Accordingly, what is claimedis:

l. A chromatographic device comprising a plate member having opposedfront and rear major faces and a peripheral edge connecting said faces,said peripheral edge including a rectilinear bottom edge portion,portions of said plate member defining a plurality of spaced channelsextending in substantially parallel relationship to each EBurke et al.,JAoAC, 49, pp. 374-385 (1.966),

other and generally perpendicular to said bottom edge portion of saidplate member, one end of each of said channels communicating with saidbottom edge portion, and a chromatographic adsorbent material carried bysaid plate member within each of said channels and extendingcontinuously over substantially the entire length of each of saidchannels.

2. The device of claim 1 wherein the maximum crosssectional area of eachof said channels is at said one end of the same.

3. The device of claim 2 wherein the maximum depth of each of saidchannels is at least in excess of 1 mm. and the minimum width of each ofsaid channels is also at least in excess of 1 mm.

4. The device of claim 1 wherein said chromatographic adsorbent isaluminum oxide G.

5. The device of claim l wherein said channels are delued as depressionsin one of said major faces, said adsorbent filling said channels andhaving an exterior surface at least substantially coplanar with said onemajor face.

6. The device of claim 5 wherein each of said channels is rectangular incross-section.

7. The device of claim 6 wherein each of said channels have a depth ofat least about 2 mm. throughout their length.

References Cited UNITED STATES PATENTS 3,194,400 7/1965 Herndon ZIO-198X 3,279,307 10/1966 Wilks 210-198 X 3,298,527 1/1967 Wright 210-1983,413,842 12/1968 Hecker 210-198 SAMIH N. ZAHARNA, Primary Examiner U.S.Cl. X.R.

ZPO- 31, 198

